Optical Coherence Tomography (OCT) is a technique for the generation of medical images that can provide axial information at a high resolution using a broadband light source and an interferometric detection system. It has found a wide range of uses, from cardiology to ophthalmology and gynecology, or for in-vitro sectional studies of biological materials.
Axial information is obtained in OCT through interferometric methods. To generate images (2D) and volume representations (3D) of the histology of tissue, it is necessary to move the beam laterally over the area of interest. This movement has been traditionally done by means of mechanical displacement of some optical element within the system such as the waveguide in the case of fiber-based systems. Alternatively, the sample can be moved underneath a stationary beam. The most common solution utilizes a moving mirror in the beam path in the sample arm of the interferometer. Although this method is effective, it has drawbacks, especially in terms of reliability, manufacturing cost, maintenance cost, complexity of adjustment, final system size, etc. The use of MOEMS technology (Micro-opto-electromechanical systems) has been proposed and demonstrated for situations in which conventional mirrors are not acceptable, such as in catheters or laparoscopic instruments. However, these devices suffer from many of the same problems as their macroscopic versions and they pose their own challenges in terms of encapsulation, sterilization, etc.
One approach for providing a lateral scan over a sample is to use multiple beams. An example of this was proposed in patent application WO 2010/134624. Several complete interferometers working in parallel are described that only share the light source. As such, the sample arm of every interferometer consists of a single optical path and there is no multiplexing mechanism leading to a structurally complicated system.
Another patent application, WO 2004/073501, contemplates the use of multiple beams that are simultaneously incident on the sample. The aim of this application is the combination of these beams in a controlled manner through the use of modulators and phase delays. The combined illumination over the sample shows a certain interference pattern. Working with the modulators and phase delay elements, the position of the interference pattern of the illumination on the sample can be varied and, subsequently, it is possible to reconstruct a three dimensional image of the sample using signal processing techniques. The application does not use multiplexing means to distinguish light collected from a plurality of optical paths. There is only a single optical path that collects the light reflected from the sample.
In an article by Yamanari et. Al, “Full-range polarization-sensitive swept-source optical coherence tomography by simultaneous transverse and spectral modulation,” Optics Express Vol. 18, Issue 13, pp. 13964-13980, 2010, a polarization sensitive SS-OCT system (Swept Source OCT) is described. In this system, and with the aim of solving the problem of complex conjugates typical of SS-OCT and FD-OCT systems (Fourier Domain OCT), phase modulation is applied to the reference arm. This phase is modified while electro-mechanical means scan the sample laterally. This document, therefore, does not describe the use of modulation in the sample arm. Moreover, in the case of Time Domain OCT systems (TD-OCT), the scanning speed of the variable delay element in the reference arm can be a limitation of the final system performance, to the extent that its operating speed or maximum scanning range may be insufficient for the application of interest. U.S. Pat. No. 6,198,540 and patent application EP 1780530 each describe systems that use multiple optical paths in the reference arm. However, each system uses traditional free space optics and mechanical means for the lateral scan of the sample.